1. Field of the Invention
This invention relates to a process method of using excimer laser for forming micro spherical and non-spherical polymeric structure array and particularly a excimer laser process to form a micro spherical array structure on a substrate for producing a metal mold to fabricate liquid crystal display (LCD) face plate or photosensitive face plate.
2. Description of the Prior Art
In order to increase visibility angle of LCD screen or other photosensitive plate, the face plate of these devices generally has to form a plurality of bulged micro spherical array structure to enhance light condensing (or dispersing) property. This micro spherical array structure usually is made by means of pressing of a metal mold. The metal mold (pressing mold) is formed by spray plating a metal layer on a main mold, then peeling off the metal layer from the main mold.
Conventionally, fabricating the main mold include the following methods:
1. Using single stepper exposure and high temperature reflow process:
xe2x80x83As shown in FIGS. 1A through 1D, this process firstly prepares a substrate 11 coated with a photoresist layer 12 (FIG. 1A). Then using a stepper 14 to proceed single stepping exposure by zones on the substrate 11 through a photomask 13 (FIG. 1B). Afterward, the non-exposure portion of the photoresist 12 is cleared through chemical agents and resulting in a micro-struts photoresist 15 array structure (FIG. 1C). Thereafter, using high temperature reflow process to heat the substrate around or exceeding the photoresist melting temperature to melt the surface of the micro-struts photoresist 15 for forming a curve shaped surface 16 (FIG. 1D).
xe2x80x83This method has the following disadvantages: 1. It needs high temperature reflow process. The process is time consuming and highly unstable. It is difficult to precisely control the spherical surface formation. 2. Stepping exposure process can only produce two dimensional (2D) strut structure, but not spherical or non-spherical three dimensional (3D) curved surfaces.
2. Multiple stepping exposure micro photo process.
xe2x80x83In the multiple stepping exposure micro process, the step 1B and 1C set forth above are repeatedly performed with different photomasks to gradually expand the exposure area of the photoresist until a pyramid-shaped photoresist structure is formed. Then the high temperature reflow process is proceeded. The reflow process may be done at a lower temperature and shorter time period. The spherical surface is also easier to control. However it has more and complicated process steps. It takes more process time and costs higher. To clean the photoresist needs a lot of chemicals and may result in severe environmental pollution problem.
3. Photosensitive glass process:
xe2x80x83As shown in FIGS. 2A and 2B, this process firstly uses an ultraviolet light source 24 (UV) to perform stepping exposure on a photosensitive glass 21 through a photomask 23 (FIG. 2A). The photosensitive glass 21 is coated with a different type of photosensitive material 22 which will be hardened and expanded upon the projection of ultraviolet light. The non-exposure portion of the photosensitive material will be squeezed and to form a bulged structure 25 (FIG. 2B).
xe2x80x83However this process also has disadvantages. For instance, the photosensitive glass is very expensive and difficult to procure. The bulged structure is also difficult to control accurately.
4. Heated dripping process:
xe2x80x83As shown in FIG. 3, this process forms the bulged 3D structure 33 by means of dripping heated photoresist 32 one by one (or multiple drops at a time) on the substrate 31. The drawback of this process is that it totally cannot control the micro spherical array structure formation.
All the conventional techniques set forth have their share of shortcomings. There is still room for improvement.
It is therefore an object of this invention to provide a process method of using excimer laser for forming spherical and non-spherical polymeric structure array that may precisely form micro spherical or non-spherical surface array structure on a substrate in a simpler and lower cost way.
It is another object of this invention to provide a process method of using excimer laser for forming spherical and non-spherical polymeric structure array that uses a photomask which has a selected curved pattern to receive excimer laser beam projection upon a polymeric material coated on a substrate. The curved pattern has different width along a straight line. The excimer laser beam hits the polymeric material and peels the material to create etching effect. During the laser beam projection and etching process, the substrate may be moved normally against the straight line direction so that the polymeric material may receive projection of different time period along the straight line direction to obtain different depth of etching for forming the 3D pattern desired.
For achieving aforesaid objects, the process of this invention includes the follow steps:
a. preparing a substrate which has a surface coating with a polymeric material and at least one photomask having a selected curved pattern formed thereon,
b. using a excimer laser beam source to project through the photomask on the polymeric material on the substrate and moving the substrate along a first corresponding direction for etching and forming a first 3D pattern on the polymeric material,
c. moving the substrate along a second corresponding direction and projecting the excimer laser beam through the photomask on the first 3D pattern to form a second 3D pattern in spherical-like manner.
In another aspect, this invention may further include the following steps:
d. using chemical etching method to remove debris of the polymeric material,
e. performing surface process to smooth the surface of the second 3D pattern,
f. spray plating a seed layer on the substrate and second 3D pattern,
g. electroplating the spray plated seed layer to form a metal layer to a selected thickness,
h. separating the metal layer from the substrate and second 3D pattern to make the metal layer become a metal mold for pressing a micro array structure.